Best-effort (BE) delivery describes a network service or link in which the network or link does not provide any guarantees that data is delivered or that a user is given a guaranteed quality of service (QoS) level or a certain priority. In a best-effort network all users obtain best-effort service, meaning that they obtain unspecified variable bit rate and delivery time, depending on the current traffic load.
These BE/non-QoS Internet Service Provider (ISP) customer connections do not prioritize different flows that originate from different “Internet sources” to the customer. This lack of prioritization causes many “real-time” packets, which need to traverse the ISP to the customer quickly, to be caught behind other customer traffic that does not have such a time sensitive delivery constraint. A bottleneck link is often the last link to the customer from a service provider and is generally a BE/non-QoS link. The packets may be dropped from the bottleneck link or a queue may form at the service provider when volume on the bottleneck link is too high.